|Publication number||US5627926 A|
|Application number||US 08/533,547|
|Publication date||6 May 1997|
|Filing date||25 Sep 1995|
|Priority date||16 Sep 1992|
|Also published as||US5467417|
|Publication number||08533547, 533547, US 5627926 A, US 5627926A, US-A-5627926, US5627926 A, US5627926A|
|Inventors||Shigeru Nakamura, Akira Arimoto, Kenkichi Suzuki, Katsuhiko Shibata|
|Original Assignee||Hitachi, Ltd.|
|Export Citation||BiBTeX, EndNote, RefMan|
|Patent Citations (9), Referenced by (59), Classifications (27), Legal Events (4)|
|External Links: USPTO, USPTO Assignment, Espacenet|
θ> 2/3×(π/2+2×arcsin (n'/n))
This is a divisional of application Ser. No. 08/117,789, filed Sep. 8, 1993, now U.S. Pat. No. 5,467,417.
The present invention relates to a prism plate which efficiently emits within a predetermined range of angles a flux of light that is incident over a wide range of angles, to an indicator, such as a liquid crystal indicator, incorporating such a prism plate that is used for information indication in information processors such as personal computers, word processors, and the like, and to an indicator illumination method which efficiently emits the flux of light within the predetermined range.
It has been desired to develop portable information processors such as personal computers and word processors, with the growth in an information-oriented society. Performance required for the portable information processors is that they should be small in size, light in weight, and consume a small amount of electric power so that they can be used for a long time on a small capacity power source.
In portable information processors, in particular, the information indicator unit roughly determines the shape of the apparatus and at ways consumes electric power; hence it is desired that such unit have a small thickness and be of a type which consumes only a small amount of electric power.
Such an indicator can be represented by a liquid crystal indicator of back-light type as described in Japanese Patent Laid-Open No. 67016/1992.
Referring to FIGS. 1 and 2 of Japanese Patent Laid-Open No. 67016/1992, the light rays emitted from light sources 23 and 24 and the light rays reflected by reflectors 25 are scattered by a scattering plate 26, pass through optical device 27 such as a prism plate whose light incident side is a flat plane 28 and whose light outgoing side is a prism plane 29, and are incident on a liquid crystal indicator element 12. In an embodiment of Japanese Patent Laid-Open No. 67016/1992, the optical device 27 such as the prism plate is made of a polycarbonate resin or a like resin, and the vertex angle between two planes of each prism on the prism plane 29 is, for example, 90 degrees (a half vertex angle is 45 degrees). The optical device 27 such as the prism plate disposed on the scattering plate 26 can collect light scattered over a wide range of angles by the scattering plate 26 in the normal direction of the optical device 27, increasing the luminance within an effective range of visual angle.
A problem arises, however, with a conventional prism plate made of a polycarbonate resin or a like resin having a vertex angle of about 90 degrees (with a half vertex angle of 45 degrees) as shown in the above-mentioned Japanese patent document.
FIG. 6 is a sectional view illustrating the conventional prism plate on an enlarged scale. Reference numeral 60 denotes a prism plate and 61 denotes a ray of light. A solid line 70 in FIG. 7 represents the visual angle characteristic of outgoing light of the prism plate 60 illustrated in FIG. 6, which characteristic is found by a ray tracing calculation under the condition where the vertex angle 2θ between a prism plane 62 and a prism plane 63 is 90 degrees (a half vertex angle θ=45 degrees) and the refractive index n is 1.585. A dotted line 71 represents the angle dependency of light intensity of the ray of light 61 incident on the prism plate 60 which corresponds to the visual angle characteristic as if there is no prism plate 60. As shown by the solid line 70 in FIG. 7, the luminance is increased by more than 1.4 times over an effective range of visual angle of from -35 degree to 35 degrees. However, the light is also emitted over ineffective ranges of visual angle from -80 degrees to -60 degrees and from 60 degrees to 80 degrees resulting in wasteful consumption of electric power. When viewed from these directions, the indicator is unnecessarily bright. The cause is attributed, as shown in FIG. 6, to the fact that the ray of light 61 incident on the prism plate 60 is totally reflected by the prism plane 62 and is emitted from the prism plane 63.
An object of the present invention is to solve the above-mentioned problems by providing an indicator which prevents light from being emitted into ineffective ranges of visual angle, so as to increase the intensity of light emitted within an effective range of visual angle. It is another object of the present invention to provide an indicator which has a small thickness and consumes a small amount of electric power, thereby being particularly suitable for portable information processors.
In order to achieve the above objects, the basic concept of the present invention is the recognition that the prism plate gathers the light from the scattering plate in the direction of an effective visual angle (for example from -60 degree to +60 degree as shown in FIG. 7), and minimizes intensity of outgoing light in the direction of a noneffective visual angle. And more desirably, the present invention is effective to assure that there is no peak of the intensity of outgoing light in the direction of the noneffective angle.
Another aspect of the present invention is a prism plate having prism-like protuberances formed at a side thereof, in which the vertex angle 2θ formed by two planes of each prism-like protuberance is defined by the formula,
where n is the refractive index of the prism plate medium.
According to yet another feature of the present invention, an data indicator for an information processor comprises a light source, a scattering plate which scatters light from the light source, an indicator plate irradiated with scattered light from the scattering plate, and a prism plate having many prism-like protuberances formed on one side thereof and being disposed between the scattering plate and the indicator plate such that the prism-like protuberances face the scattering plate, and, the vertical angle 2θ formed by two planes of each of the prism-like protuberances is,
where n is the refractive index of the prism plate, and n' is the refractive index of the material in which the prism plate is arranged.
Accordingly, in a prism plate whose prism vertex angle 2θ satisfies the above inequalities, the totally reflected scattered light from one surface of the prism-like protuberance is also totally reflected on the other surface of the prism-like protuberance, thereby making it possible to gather the emitted light only in the effective range of visual angle.
These and other objects, features and advantages of the present invention will become more readily apparent from the following detailed description when taken in conjunction with the accompanying drawing wherein:
FIG. 1 is a sectional view of a liquid crystal indicator of the side light type in accordance with one embodiment of the present invention;
FIG. 2 is an exploded perspective view of the indicator of FIG. 1 showing the liquid crystal indicator of the present invention;
FIG. 3 is an enlarged sectional view which illustrates a prism plate embodying the present invention;
FIG. 4 is a diagram showing a ray trace of the prism plate;
FIG. 5 shows the visual angle characteristic of the prism plate of the present invention;
FIG. 6 is an enlarged sectional view which illustrates a conventional prism plate;
FIG. 7 shows the visual angle characteristic of the conventional prism plate of FIG. 6; and
FIGS. 8 (a) and (b) are enlarged perspective views showing two protuberance structures at the surface of the prism plate of the type shown in FIGS. 3 and 4 in accordance with the present invention.
In FIGS. 1 and 2, reference numeral 1 denotes a cold cathode-ray tube, 2 denotes a reflector plate, and 3 denotes a lightguide plate made of an acrylic resin or the like resin and having a reflector 4 such as white paint applied to the lower surface thereof. Reference numeral 5 denotes a thin scattering plate having fine roughness on the surface thereof which is placed on the upper surface of the lightguide plate 3, reference numeral 6 denotes a prism plate whose lower side is flat and which has prism protuberances formed on the upper side thereof, and reference number 7 denotes a liquid crystal indicator element.
The principle of the present invention will be described with reference to FIG. 4 which is a ray-trace diagram of light of the prism plate. Reference numeral 40 denotes a prism plate having a vertex angle between a prism plane 42 and a prism plane 43 of 2θ (a half vertex angle is θ) and a refractive index of n, and 41 denotes a ray of light having an angle of incidence of α (the direction indicated by arrow in FIG. 4 is assumed to be negative). The angle of refraction α' on a plane 44 (direction indicated by arrow in FIG. 4 is assumed to be negative) and the angle of incidence β on the prism plane 42 (direction indicated by arrow in FIG. 4 is assumed to be negative) are given by:
α'=arcsin(1/n×sinα) . . . (1)
β=α'+θ-π/2 . . . (2)
The ray of light that satisfies the condition of n×sin/β<-1 is totally reflected by the prism plane 42 and is incident on the prism plane 43. The angle of incidence δ on the prism plane 43 is given as the following formula:
δ=-β-2θ. . . (3
As the incidence α becomes smaller, the incidence β becomes larger. The smallest angle of incidence α is -π/2. So if sin α is -1 and if
n×sinδ<-1 . . . (4)
then, the rays of light incident on the prism plane 43 are all totally reflected, emitted from the plane 44 of the prism plate 40, scattered by the scattering plate and the like, and become rays of light that are incident again on the prism plate 40. When this inequality is transformed,
δ<arcsin (-1/n) . . . (5)
Based on formulas (3) and (5),
β>2θ+arcsin (1/n) . . . (6)
Based on formulas (2) and (6),
θ>1/3×(π/2+arcsin (1/n)-α') . . . (7)
Moreover, α'=-arcsin (1n) since sin α=-1
2θ>2/3(π/2+2×arcsin (1/n)) . . . (8)
Accordingly, in a prism plate whose prism vertex angle 2θ satisfies the above inequality (8), the totally reflected scattered light from the surface 42 is also totally reflected on the surface 43. And such prism plate makes it possible to prevent the light from being emitted in the ineffective range of visual angle that has been a problem inherent in the prior art, and further makes it possible to utilize the light that has hitherto been emitted to ineffective ranges of visual angle, as incident light that falls on the prism plate. This enables the light intensity within an effective range of visual angle to be increased substantially more than that of the prior art.
In the above explanation, the material around the prism plate is, for example, air or vacuum whose refractive index is 1. If the material around the prism plate is another material (for example, liquid such as oil or water, or transparent solid matter such as resin or glass) whose refractive index is n', the inequality (8) should be rewritten to inequality (9) as follows;
2θ>2/3(π/2+2×arcsin(n'/n)) . . . (9)
Because, when the light irradiated from a material 1 (whose refractive index is n1) to a material 2 (whose refractive index is n2), the relative refractive index n21 is n2 /n1. We can obtain formula (9) by rewriting "1/n" to "n'/n" in formula (8).
Next, described below is the operation of the liquid crystal indicator element of this embodiment. The light emitted from the cold cathode-ray tube 1 is incident on the side surface of the lightguide plate 3 directly or after-reflected from the reflector plate 2, reflected by the reflection member 4 applied to the lower side of the lightguide plate 3, and emitted from the upper side of the lightguide plate 3. The light emitted from the lightguide plate 3 is distributed through the scattering plate 5, and hence the light intensity is of a uniform distribution over a wide range of angles. The prism plate 6 utilizing the principles of the present invention emits light only within an effective range of visual angle, so that information is indicated through the liquid crystal indicator element 7.
FIG. 3 is an enlarged sectional view of the prism plate 6. In this embodiment, the prism plate 6 is made of an acrylic resin and has a refractive index n of 1.585. By substituting the refractive index n=1.585 of the prism plate 6 for the right side of the inequality (8),
2/3 (π/2+2×arcsin (1/n))=112.2 degrees
Therefore, the inequality (8) becomes,
Thus, the vertex 2θ of the prism formed on the upper side is set to an angle which is greater than 112.2 degrees. For instance, 120 degrees (half vertex angle θ is 60 degrees) is desirable. Moreover, the pitch P of the prism is, for example, 50 μm. In FIGS. 1 to 3, the shapes of the prisms are shown in an exaggerated manner with respect to the thickness of the prism plate. The prism plate has a thickness of, for example, 1 min.
A solid line 50 of FIG. 5 represents the visual angle characteristic of the outgoing light of the prism plate 6 found by the ray trace calculation, similar to that of FIG. 7. Furthermore, a dotted line 71 corresponds to the visual angle characteristic of the scattering plate 5 as would occur when there is no prism plate 6, similar to that of FIG. 7, and shows a uniform distribution of light intensity over a wide range of angle of about +/-(plus/minus) 80 degrees. As shown by the solid line 50 in FIG. 5, no light is emitted over ineffective ranges of visual angle of smaller than -60 degrees and greater than 60 degrees, and the electric power is thus not wastefully consumed. Even when viewed from these directions, the indicator is not unnecessarily bright. Moreover, the effective range of visual angle is +/-45 degrees which is wider than the effective range of visual angle of +/-35 degrees as shown by the solid line 70 of FIG. 7, and the luminance is increased by more than 1.4 times.
The present invention is in no way limited only to the above-described embodiment, and the prism plate need only have a refractive index and a vertex angle which satisfy the inequality (8). Furthermore, the prism plate is not limited to the one that has a prism shape only in one direction as shown in FIGS. 1 and 2, but can be those of a pyramid shape as shown in FIG. 8(a) or a conical shape having a prism shape in cross section in two directions, which is shown in FIG. 8(b). Moreover, the invention is not limited to the specific features shown in FIGS. 1 and 2, but can also include an embodiment in which the positions of the prism plate and the liquid crystal indicator element are exchanged. It is also within the scope of the present invention that the indicator can be a liquid crystal indicator of the back-light type as shown in FIGS. 1 and 2 of Japanese Patent Laid-Open No. 67016/1992.
In summary, the present invention provides an indicator which prevents light from being emitted into ineffective ranges of visual angle, increases the intensity of light emitted within an effective range of visual angle, has a small thickness and consumes a small amount of electric power, and hence is particularly suitable for use in a portable information processor,
Although the invention has been ,described and illustrated in detail, it is to be clearly understood that the same is by way of illustration and example, and is not to be taken by way of limitation. The spirit and scope of the present invention are to be limited only by the terms of the appended claims.
|Cited Patent||Filing date||Publication date||Applicant||Title|
|US5050946 *||27 Sep 1990||24 Sep 1991||Compaq Computer Corporation||Faceted light pipe|
|US5211463 *||11 Mar 1992||18 May 1993||Kaiser Aerospace & Electronics Corporation||Backlight for liquid crystal devices|
|US5237641 *||23 Mar 1992||17 Aug 1993||Nioptics Corporation||Tapered multilayer luminaire devices|
|US5303322 *||11 Mar 1993||12 Apr 1994||Nioptics Corporation||Tapered multilayer luminaire devices|
|US5339382 *||23 Feb 1993||16 Aug 1994||Minnesota Mining And Manufacturing Company||Prism light guide luminaire with efficient directional output|
|US5353133 *||18 Jan 1994||4 Oct 1994||Magnascreen Corporation||A display having a standard or reversed schieren microprojector at each picture element|
|US5359691 *||19 Apr 1993||25 Oct 1994||Briteview Technologies||Backlighting system with a multi-reflection light injection system and using microprisms|
|US5467417 *||8 Sep 1993||14 Nov 1995||Hitachi, Ltd.||Prism plate for efficiently emitting light flux within a predetermined range, and liquid crystal indicator and indicator illumination method using the same|
|US5479275 *||3 Dec 1993||26 Dec 1995||Ois Optical Imaging Systems, Inc.||Backlit liquid crystal display with integral collimating, refracting, and reflecting means which refracts and collimates light from a first light source and reflects light from a second light source|
|Citing Patent||Filing date||Publication date||Applicant||Title|
|US5818555 *||2 Nov 1994||6 Oct 1998||Enplas Corporation||Surface light source device|
|US5854872 *||8 Oct 1996||29 Dec 1998||Clio Technologies, Inc.||Divergent angle rotator system and method for collimating light beams|
|US6025897||27 Nov 1996||15 Feb 2000||3M Innovative Properties Co.||Display with reflective polarizer and randomizing cavity|
|US6099135 *||31 Jan 1997||8 Aug 2000||Mitsubishi Rayon Co., Ltd.||Surface light source element and liquid crystal display device, sign device and traffic control sign device using same|
|US6104455 *||7 Aug 1998||15 Aug 2000||Dai Nippon Printing Co., Ltd.||Back light device and liquid crystal display apparatus|
|US6147725 *||20 Oct 1998||14 Nov 2000||Mitsubishi Denki Kabushiki Kaisha||Liquid crystal panel module with polarization transformation for increased brightness|
|US6231200 *||11 Oct 1996||15 May 2001||Omron Corporation||Surface light source device, elements therefor and apparatus using the same|
|US6244719||15 Dec 1999||12 Jun 2001||Mitsubishi Rayon Co., Ltd.||Surface light source device and liquid crystal display device sign display apparatus and traffic sign display apparatus using the surface light source device|
|US6332691||16 Apr 2001||25 Dec 2001||Mitsubishi Rayon Co., Ltd.||Surface light source device, and liquid crystal display device, sign display apparatus and traffic sign display apparatus using the surface light source device|
|US6354709||5 Apr 2000||12 Mar 2002||3M Innovative Properties Company||Optical film|
|US6356391||8 Oct 1999||12 Mar 2002||3M Innovative Properties Company||Optical film with variable angle prisms|
|US6447135||8 Oct 1999||10 Sep 2002||3M Innovative Properties Company||Lightguide having a directly secured reflector and method of making the same|
|US6502947 *||30 Mar 2001||7 Jan 2003||Mitsubishi Rayon Co., Ltd.||Planar light source device and liquid crystal display apparatus|
|US6560026||16 Jan 2002||6 May 2003||Mark E. Gardiner||Optical film with variable angle prisms|
|US6578976 *||10 Aug 2001||17 Jun 2003||Klaus Bothe||Lighting device|
|US6581286||16 Jan 2002||24 Jun 2003||3M Innovative Properties Company||Method of making tool to produce optical film|
|US6707611||29 Jan 2003||16 Mar 2004||3M Innovative Properties Company||Optical film with variable angle prisms|
|US6819372||29 Feb 2000||16 Nov 2004||Dai Nippon Printing Co., Ltd.||Back light device with diffusing sheet for a liquid crystal display apparatus|
|US6845212||8 Oct 1999||18 Jan 2005||3M Innovative Properties Company||Optical element having programmed optical structures|
|US6903788||3 Jul 2002||7 Jun 2005||Nitto Denko Corporation||Optical film and a liquid crystal display using the same|
|US6955460 *||17 Dec 2002||18 Oct 2005||Lg.Philips Lcd Co., Ltd.||LCD backlight unit having 40° half power angle without a polarizing sheet|
|US7046905||11 Jul 2000||16 May 2006||3M Innovative Properties Company||Blacklight with structured surfaces|
|US7056005 *||10 Jul 2002||6 Jun 2006||Samsung Electronics Co., Ltd.||Light guiding plate having brightness enhancement recesses|
|US7077544 *||6 May 2003||18 Jul 2006||Solid State Opto Limited||Light emitting panel assemblies|
|US7147358||31 Dec 2003||12 Dec 2006||3M Innovative Properties Company||Cover removal tab for optical products|
|US7221847||3 Aug 2004||22 May 2007||3M Innovative Properties Company||Optical elements having programmed optical structures|
|US7236217||16 Jan 2003||26 Jun 2007||3M Innovative Properties Company||Package of optical films with zero-gap bond outside viewing area|
|US7278771||22 Nov 2004||9 Oct 2007||3M Innovative Properties Company||Optical film|
|US7339635||14 Jan 2005||4 Mar 2008||3M Innovative Properties Company||Pre-stacked optical films with adhesive layer|
|US7407317||22 Dec 2005||5 Aug 2008||Lg Display Co., Ltd.||Prism sheet and backlight unit using the same|
|US7413336||29 Aug 2003||19 Aug 2008||3M Innovative Properties Company||Adhesive stacking for multiple optical films|
|US7431493||5 Jun 2006||7 Oct 2008||Samsung Electronics Co., Ltd.||Light guiding plate with brightness enhancement means and liquid crystal display|
|US7520654||7 Jul 2008||21 Apr 2009||3M Innovative Properties Company||Adhesive stacking for multiple optical films|
|US7664350||9 Sep 2008||16 Feb 2010||Banyan Energy, Inc.||Compact optics for concentration, aggregation and illumination of light energy|
|US7672549||10 Sep 2007||2 Mar 2010||Banyan Energy, Inc.||Solar energy concentrator|
|US7777832||18 Nov 2005||17 Aug 2010||3M Innovative Properties Company||Multi-function enhancement film|
|US7852560||4 Dec 2008||14 Dec 2010||3M Innovative Properties Company||Display incorporating reflective polarizer|
|US7873256||14 Sep 2005||18 Jan 2011||3M Innovative Properties Company||Backlight with structured surfaces|
|US7925129||12 Feb 2010||12 Apr 2011||Banyan Energy, Inc.||Compact optics for concentration, aggregation and illumination of light energy|
|US8319764||27 Nov 2012||Research In Motion Limited||Wave guide for improving light sensor angular response|
|US8403539||26 Feb 2010||26 Mar 2013||Research In Motion Limited||Light guide for improving device lighting|
|US8412010||4 Nov 2010||2 Apr 2013||Banyan Energy, Inc.||Compact optics for concentration and illumination systems|
|US8588574||30 Oct 2007||19 Nov 2013||3M Innovative Properties Company||Backlight with structured surfaces|
|US8705914||26 Oct 2011||22 Apr 2014||Banyan Energy, Inc.||Redirecting optics for concentration and illumination systems|
|US20040141103 *||16 Jan 2003||22 Jul 2004||Kotchick Keith M.||Packaging and handling method for optical films|
|US20040196645 *||29 Oct 2001||7 Oct 2004||Heather Allinson||Edge lit illumination devices|
|US20050001043 *||3 Aug 2004||6 Jan 2005||3M Innovative Properties Company||Optical elements having programmed optical structures|
|US20050046767 *||29 Aug 2003||3 Mar 2005||Freking Anthony J.||Adhesive stacking for multiple optical films|
|US20050134963 *||6 Jan 2005||23 Jun 2005||3M Innovative Properties Company||Method for stacking surface structured optical films|
|US20050146881 *||31 Dec 2003||7 Jul 2005||Freking Anthony J.||Cover removal tab for optical products|
|US20050238852 *||23 Apr 2004||27 Oct 2005||Naoki Nakayama||Optical products for displays|
|US20050270439 *||26 Jul 2005||8 Dec 2005||3M Innovative Properties Company||Display having a reflective polarizer|
|US20110241977 *||1 Apr 2010||6 Oct 2011||Microsoft Corporation||Enhanced viewing brightness for surface display|
|US20120069597 *||19 Mar 2010||22 Mar 2012||Naoya Sone||Planar light source device having light guide plate with reflective member|
|CN100427976C||26 Dec 2005||22 Oct 2008||乐金显示有限公司||Prism sheet and backlight unit using the same|
|DE102005061307B4 *||21 Dec 2005||15 May 2008||Lg. Philips Lcd Co., Ltd.||Prismenlage und Hinterleuchtungseinheit unter Verwendung derselben|
|EP1055944A1 *||23 May 2000||29 Nov 2000||Nitto Denko Corporation||Polarizing element and optical element|
|EP2362250A1 *||26 Feb 2010||31 Aug 2011||Research In Motion Limited||Light guide for improving device lighting|
|WO1998015862A1 *||1 Oct 1997||16 Apr 1998||Clio Tech Inc||A divergent angle rotator system and method for collimating light|
|U.S. Classification||385/36, 362/302, 385/147, 359/834, 362/620, 349/113, 362/309, 385/37, 362/561, 349/112, 385/901, 349/62, 362/23.17, 362/23.15|
|International Classification||G02F1/1335, G02B6/00, G02F1/13357, G02B5/04, F21V8/00, F21V5/02|
|Cooperative Classification||Y10S385/901, G02B6/0053, G02B6/0043, G02B6/0036, F21V5/02|
|European Classification||G02B6/00L6O8P, F21V5/02|
|12 Sep 2000||FPAY||Fee payment|
Year of fee payment: 4
|29 Sep 2004||FPAY||Fee payment|
Year of fee payment: 8
|24 Sep 2008||FPAY||Fee payment|
Year of fee payment: 12
|12 Dec 2011||AS||Assignment|
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